This invention relates to a rigid polyurethane foam which has excellent physical properties, does not contain particularly a surface void and shows only slight expansion after molding; a process for producing such a rigid polyurethane foam; and products obtained by application of such a rigid polyurethane foam.
Rigid polyurethane foams are usually obtained by reacting a polyol component and an isocyanate component in the presence of a blowing agent, a reaction catalyst and a foam stabilizer. In general, for obtaining a closed-cell rigid polyurethane foam excellent in heat-insulating properties with high productivity, there is conventionally used, as the above blowing agent, trichloromonofluoromethane having excellent characteristics, for example, in that it gives a very low thermal conductivity of gas, has a low boiling point, and is liquid at ordinary temperature, noncombustible and low in toxicity. As a prior art reference concerning a production process of such a rigid polyurethane foam, there is known, for example, Japanese Patent Unexamined Publication No. 59-84913.
Trichloromonofluoromethane (CCl.sub.3 F) conventionally used as the blowing agent is one of hardly decomposable CFC's (an abbreviation of chlorofluorocarbons; substituted hydrocarbons having chlorine and fluorine as the substituents). It is considered that when such a hardly decomposable CFC is released into the atmosphere, it acts to destroy the ozone layer in the stratosphere or cause rise of earth surface temperature due to so-called greenhouse effect. Thus, employment thereof has posed a global environmental pollution problem in recent years. In the future, the production and consumption of the hardly decomposable CFC's are to be restricted in stages, and a method for reducing their use is a serious problem. Therefore, substitutes for the hardly decomposable CFC's are being chosen all over the world. As hopeful substituents, there have been proposed 1,1-dichloro-2,2,2-trifluoroethane and 2,2-dichloro-2-monofluoroethane which are easily decomposable HCFC's (hydrochlorofluorocarbons). However, although there have been investigated various rigid polyurethane foams obtained by use of these compounds, there has not yet been obtained a rigid polyurethane foam having a good balance in physical properties, in particular, such a polyurethane foam which has no surface void and shows only slight expansion after molding.